Invisible audiences: While we can visually detect most people who can overhear our speech in unmediated spaces, it is virtually impossible to ascertain all those who might run across our expressions in networked publics. This is further complicated by the other three properties, since our expression may be heard at a different time and place from when and where we originally spoke.

boyd, danah. (in press) “Why Youth (Heart) Social Network Sites: The Role of Networked Publics in Teenage Social Life.” MacArthur Foundation Series on Digital Learning, Identity Volume (ed. David Buckingham).